I just swapped my stock 370Z muffler with a G37 coupe muffler. The G37 muffler has the same dimensions as the 370Z muffler except for the longer tips. That means you can just bolt the muffler on without modifying anything else. The tips are about 2 inches longer on the G37, so it will be sticking out of the 370 bumper. It actually looks pretty good with the tips sticking out.
By changing the muffler, I finally got the famous VQ sound. I love that hollow, throaty, Chewbacca tone of the 350Z, G35, and G37. It's a shame that the stock 370Z muffler didn't retain that sound due to noise ordinances. Currently I'm running a non-resonated midpipe. Once I find a stock resonated midpipe, I will put a video up.
I recommend this muffler swap for anyone who wants a better sounding exhaust for cheap (~$200 installed). You have to buy the coupe version, and if its from a 2008 model make sure it had the rattle issue resolved (it was a TSB). There will be no horsepower gain with this setup. In fact, you will probably lose 2 horsepowers based on the G37 being rated as 330 hp. But it's worth it to me cuz I LOVE that old VQ sound.